1. Field of the Invention
The present invention relates to a process for preparing 3-pentenenitrile.
2. Description of Related Art
Adiponitrile is an important starting material in nylon production and is obtained by double hydrocyanation of 1,3-butadiene. In a first hydrocyanation, 1,3-butadiene is hydrocyanated to 3-pentenenitrile, and the by-products obtained are mainly 2-methyl-3-butenenitrile, 4-pentenenitrile, 2-pentenenitriles, 2-methyl-2-butenenitriles, C9 nitriles and methylglutaronitrile. In a second, subsequent hydrocyanation, 3-pentenenitrile is reacted with hydrogen cyanide to give adiponitrile. Both hydrocyanations are catalyzed by nickel(0)-phosphorus complexes.
For the second hydrocyanation, it is essential that the 3-pentenenitrile used is free of 2-methyl-3-butenenitrile, since 2-methyl-3-butenenitrile is otherwise hydrocyanated to the undesired by-product methylglutaronitrile.
A general review of nickel-catalyzed olefin hydrocyanation is given in Tolman et al., Adv. Cat. 33, 1-46 (1985).
The hydrocyanation of 1,3-butadiene using a nickel catalyst of the formula Ni[P(OR)3]4 is described in U.S. Pat. No. 3,496,215. A disadvantage of this process is that no suitable technique for fully recovering the 1,3-butadiene or the catalyst is specified.
U.S. Pats. No. 5,693,843, 5,696,280, 5,821,378 and 5,981,772 describe hydrocyanations of 1,3-butadiene with multidentate phosphorus ligands, although no suitable procedure for the recovery of the catalyst components is shown in the individual embodiments.
The performance of the hydrocyanation in one or more reactors and their connection is described in U.S. Pat. No. 4,810,815, and the possibility is mentioned of continuous operation of stirred tanks or batteries of stirred tanks, but only a semibatch mode is described in detail in examples, from which it cannot be directly discerned by those skilled in the art under which conditions the method has to proceed in continuous stirred tanks.
A process for removing organic phosphorus compounds and their metal complexes from organic nitriles in the hydrocyanation of olefins is described in U.S. Pat. No. 3,773,809. The removal is effected by contacting the product with a cycloparaffin or a paraffinic hydrocarbon. This forms a liquid multiphasic system. This method of removing and recovering catalyst components by extraction cannot be applied in the hydrocyanation of 1,3-butadiene owing to the concentration of dinitriles in the reaction product being too low.